Parasites, those little bugs that infest your pet. We’re going to talk about the ones that attack from the inside. We’ll get to the ones on the outside next.

When your veterinarian asks you to bring in a fecal sample for testing I promise you it’s not because we like the smell. Fecal samples are most often used to perform a fecal floatation test. In this test the samples typically have specific fluid added to them, they are spun in a centrifuge then left to sit for some time allowing parasite eggs to collect at the top of the fluid. In this way we get the best chance to find eggs, cysts and sometimes the infective agents themselves. Fecal samples can also be used for direct smears and other testing if required.

Caveat to the following article. The information being given is basic in nature so that you have a basis to understand results given to you by your veterinarian. As in any case of disease (parasitic or otherwise) discuss test results and treatments with your doctor.

Let’s talk about the most common parasites found during this routine test.

Coccidia (protozoan parasite)

Infection of this little periodic troublemaker comes primarily from ingesting the oocytes (eggs) in infected feces. This typically occurs in environments that are not being cleaned properly. That said, the majority of coccidia infections are non-disease causing.

If disease is present there are typically other factors along with the coccidia themselves. These include stress, malnutrition, overcrowding and unhygienic conditions. Clinical signs start with diarrhea (watery, sometimes with blood). Other signs can include weight loss, energy level decreasing and possible vomiting. The majority of animals that show clinical signs are puppies as their immune systems are still immature.

Because coccidia can be found in asymptomatic animals (those not showing any signs of disease) treating just on the presence of it in a fecal floatation is not always warranted. Often these will be self-limiting infections. However, if there are multiple animals in the home treating can help reduce contamination in the environment.

There are many drug treatments for coccidia (the most common being sulfa containing antibiotics) and this should be discussed with your veterinarian.

Giardia (protozoa parasite)

Giardia are pear shaped protozoa that infect the small intestine leading to poor absorption and possible diarrhea. Animals are typically infected by consuming contaminated food or water. Again puppies are most commonly infected along with animals in groups that are kept in small areas.

Clinical signs are characterized by diarrhea which can be persistent, intermittent, start acutely or last chronically.

Giardia can be diagnosed with fecal floatation or, more commonly, by a test for the Giardia antigen.

Treatment is often with a combination of antibiotics and anti-parasitic agents. However, failure to respond to initial treatment is common. Animals will shed infective cysts and can recontaminate themselves and other animals in the house. Along with medical treatment the patient should be bathed frequently to help remove cysts from fur, clean environment often and well, discuss treating animals that are housed together. As always, discuss treatment with your vet.

A whole mess of worms


Or Ascarids. These are the most common type of intestinal parasite in dogs and cats. Typically seen in puppies or kittens. Infection can occur from ingestion of eggs, ingestion of an intermediate host or even infection via mother’s milk or through the placenta (depending on which species of worm).

They cause discomfort of the stomach, potbellied appearance, diarrhea and poor growth. On very rare occasions large numbers can cause an intestinal foreign body, intussusception (when the intestine telescopes in on itself) or intestinal perforation.

It is easily diagnosed by fecal examination.


Hookworms attach by mouthparts in the intestine to suck blood and other fluids. As they move along to eat they leave bleeding ulcers. Infection can occur similarly to the roundworms above. The eggs from the adult worms pass into the feces and are then ingested by another host.

Signs of hookworm infestation include anemia, lethargy, pale gums and dehydration.

Again, hookworms can be readily diagnosed by fecal floatation.

Bad news time: both ascarids and hookworms can be zoonotic (fancy word for a disease that can infect both animals and humans). Hooks cause a disease called Cutaneous Larva Migrans. Infection in humans is on the skin, very itchy, and usually treatable. This is one of the reasons that dogs are often banned from public places (beaches/parks etc.). The good news is, however, hookworm eggs do not last long in the environment (lasting only a few months) are do not survive freezing. Bleach will destroy the eggs outer coating leading them to dehydrate and die quicker.

Ascarid eggs if ingested by humans can lead to the larva migrating to the eyes, neurological tissue or other internal organs. The damage done can be permanent, the disease signs depending on which tissue is affected. Roundworms are much hardier in the environment so treatment/prevention is very important.

The good news is that both Ascarids and Hookworms are easily treated with de-worming agents and by your pets monthly heartworm pill (another good reason to give heartworm prevention). Also this is why puppies should be started on a broad deworming medication (one that treats for many species) starting at 2 weeks old. They should then be given a dose every 2 weeks until 8 weeks old when the owner should be bringing their new pups to the vet for a first time and have a fecal sample checked.


As with other internal parasites, whipworms primarily cause diarrhea (sometimes with blood present). In very rare cases severe infestations can lead to electrolyte disturbances. 

Whipworm eggs are not infective when they are excreted, it takes 2-3 weeks for them to become and infective (larval) stage. When the dog or cat ingests the larval eggs they mature first in the small intestine, moving finally to the large intestine. Adults produce eggs for 70-90 days, intermittently. This means that whips cannot be ruled out as a cause of diarrhea even if the fecal sample is negative. It also means that careful cleaning of the environment is essential in preventing reinfection.

Diagnosis is via fecal floatation, the eggs are characteristically barrel shaped.

Treatment is via de-wormer (typically given for 3-5 days then repeated at 3 weeks and 3 months due to the long lifecycle). But in good news there is a heartworm product that treats whipworms too. Sentinel (from Novartis) has an active ingredient that treats for this worm. If your dog is on another heartworm prevention product and is positive for whipworms it is advisable to switch.


 Tapeworms rarely cause severe disease if any signs are seen a slight loss is overall body condition is the most likely.

 Infection occurs from ingesting the intermediate host (most often fleas or lice) where the eggs have started to mature.

Identification of infection is most often brought to vets attention when the owner notices “rice segments” in the animal’s feces.

They are easily treated with deworming agents but the most important factor in preventing reinfection is good flea control.

One final species to mention is Strongyloides or threadworms. This is an uncommon disease in dogs and cats leading to no clinical signs in a light infection to diarrhea in heavy ones. It is important to mention because it is another zoonotic agent. It can be difficult to treat. If your animal is positive for this infection your vet will have more information in terms of treatment/environmental control and helping to prevent reinfection.

Last tip-and I’m hoping this did not need to be said but you never know. Due to the fact that some of these worms can affect you too ALWAYS follow good sanitary policies. In other words WASH YOUR HANDS after touching your dog’s rear end and/or feces. Especially with young puppies/kittens who are more likely to be harboring infections. is a good source for more information.

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